The invention relates to a method for processing reinforced polymer, reinforced polymer made by said method, and tires made using said reinforced polymer.
The use of macro short fiber (0.05 mm to 10 mm in length with an aspect ratio of 50-100) reinforced polymers to make V-belts, tires and other composite polymer articles is well known in the art. Such prior art composites comprise a rubber composition (for example styrene butadiene rubber (SBR), polyisoprene, polybutadiene, polychloroprene, nitrile butadiene rubber (NBR), ethylene propylene diene monomer rubber (EPDM), natural rubber and mixtures thereof), which has been loaded with chopped or crushed fiber made from, for example, spun polyaramide (e g. Kevlar.RTM., available from E.I. Dupont de Nemours & Company, Inc., Wilmington, Del.), spun amide, spun nylon 6 (1,6 polycaprolactam available from Allied Chemical, Morristown, N.J.), polybenzimidazole fibers, spun polyesters (e.g. polyethylene terephthalate (PET), also available from Allied Chemical).
It is also known in the prior art that it is difficult to mix most macro fibers into a rubber compound since the fibers have a tendency to mat and good dispersion requires many mixing steps. Also, macro fiber loading may limit the usefulness of a composite rubber for certain applications since a rubber loaded with macro fibers cannot be extruded to the small dimensions required for use in an apex, for example (i.e. because of the macro fiber, the rubber cannot be feathered to the small dimension required in the peak of the apex.)
Kevlar.RTM., for example, is ordinarily mixed at a maximum useful load of about six (6) phr (6 parts by weight per hundred parts by weight rubber). It is known in the prior art to load a rubber compound with about 15-40 phr Kevlar.RTM. when used in a V-belt or hose, where no small dimensions of rubber are required.
Micro fibers (0.1 um to 10 um in length with an aspect ratio of 1-5) can be formed in situ or dispersed in a polymer matrix. (When incorporated into an article of manufacture, the micro fibers may be further elongated, the amount of elongation depending on the manner in which the rubber composite is processed.) Isayev et al, for example, in U.S. Pat. No. 4,728,698, teach the in-situ formation of fibers in a polymer matrix by the addition of a liquid crystal polymer to a base polymer followed by mixing and extrusion.
It has been shown that the orientation of macro fibers in a polymer matrix can be controlled by the mixing and/or extrusion of a base polymer containing such fibers. The orientation of fibers in a polymer matrix improves the modulus (stiffness) of the polymer in the direction parallel to the direction of orientation. The presence of fibers also improves the cut resistance properties, load bearing properties, and green strength of the polymer. On the other hand, composites loaded with macro fibers tend to have a relatively higher hysteresis, which might limit the efficiency of the composite, especially when used in rubber articles that undergo large numbers of flexes in use.
Orientation of micro fibers is more difficult to obtain, but even so, micro fiber composites without anisotropy improve the stiffness of a rubber compound while contributing little to the hysteresis of the compound. Micro fiber loaded composites have a lower hysteresis than comparable composites loaded with carbon black or macro fibers.
Accordingly, it is an object of the present invention to provide a method by which the properties of a rubber composite can be optimized for a particular use by adjusting the amount of macro fibers, micro fibers and other reinforcing fillers (such as carbon black, silica, etc.) in the composite. It is a further object of the invention to provide a rubber composite with a reduced macro fiber load which has properties substantially equivalent to a prior art composite having a higher macro fiber load by replacing some of the macro fibers with micro fibers. The method simplifies mixing macro fibers into the composite since lower concentrations of macro fibers are used, and the compound therefore is easier to mix.
Additional objects are to provide a new polymer blend that includes macro fibers and micro fibers, and elastomeric products incorporating such a polymer blend.
Other objects of the invention will be apparent from the following description.